The Weather of October 2018

With the northeast monsoon successively affecting south China coastal areas, October 2018 was slightly cooler than usual in Hong Kong. The monthly mean temperature of 25.3 degrees was 0.2 degrees below the normal figure of 25.5 degrees. The monthly rainfall was 104.3 millimetres, slightly above the normal of 100.9 millimetres in October. The accumulated rainfall recorded in the first ten months of the year was 2077.6 millimetres, a deficit of 11 percent compared to the normal of 2334.0 millimetres for the same period.

Under the influence of the northeast monsoon, apart from a few morning showers on 1 October, the local weather was generally fine and dry on 1 - 8 October. With abundant sunshine, temperatures at the Hong Kong Observatory rose to 31.4 degrees on the afternoon of 5 October, the highest of the month. Affected by an easterly airstream, there were sunny periods and a few showers on 9 October.

A cold front crossed the coastal areas of Guangdong on the afternoon of 10 October. Heavy showers associated with the cold front brought more than 20 millimetres of rainfall to most parts of the territory in the afternoon, rainfall even exceeded 40 millimetres in the urban areas and Shek Kong. The northeast monsoon brought mainly cloudy and cooler weather as well as a few rain patches to Hong Kong in the next four days. With an easterly airstream setting in, it was cloudy with showers on 15 October.

A weak cold front crossed the coast of Guangdong on the morning of 16 October. The associated northeast monsoon brought some rain and slightly cooler weather to Hong Kong on 16 - 17 October. Under the influence of a strong easterly airstream, it was windy and cooler with rain patches on 18 October. The temperature of the Observatory dropped to 20.9 degrees under the rain on the morning of 18 October, the lowest of the month. Apart from a few rain patches, local weather became gradually brighter during the day on 19 - 20 October.

Dominated by an anticyclone aloft southern China, local weather became generally fine on 21 October and the next morning. With a weak northeast monsoon arriving at the coast of Guangdong on 22 October, local weather turned mainly cloudy with light rain patches in the afternoon and the next two days. Under the influence of anticyclone aloft, the weather in Hong Kong became brighter with sunny periods on 25 - 26 October. A cold front moved across the coastal areas of Guangdong on the night of 26 October. Under the influence of the dry northeast monsoon, the weather in Hong Kong became fine and very dry with cooler mornings on 27 - 30 October. Meanwhile, tropical cyclone Yutu entered the northern part of the South China Sea and edged closer to the coast of Guangdong on 31 October. Locally, it was very dry with winds picking up gradually from the north on that day.

Three tropical cyclone occurred over the South China Sea and the western North Pacific in the month.

Details of issuance and cancellation of various warnings/signals
in the month are summarized in Tables 1.1 to 1.4. Monthly meteorological
figures and departures from normal for October are tabulated in Table 2.

Warnings and Signals issued in October 2018

Table 1.1 Tropical Cyclone Warning Signals

Name ofTropical Cyclone

SignalNumber

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

YUTU

1

31 / 10

0840

1 / 11

1240

Table 1.2 Strong Monsoon Signal

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

18 / 10

2220

20 / 10

0945

Table 1.3 Thunderstorm Warning

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

10 / 10

1257

10 / 10

1600

Table 1.4 Fire Danger Warnings

Colour

Beginning Time

Ending Time

Day/Month

HKT

Day/Month

HKT

Yellow

1 / 10

0910

1 / 10

2000

Red

3 / 10

1240

3 / 10

1940

Red

4 / 10

0800

6 / 10

2100

Yellow

7 / 10

0600

7 / 10

1800

Yellow

14 / 10

0740

14 / 10

1800

Yellow

21 / 10

0745

21 / 10

1800

Yellow

27 / 10

0600

28 / 10

0600

Red

28 / 10

0600

1 / 11

1900

Table 2 Figures and Departures from Normal - October 2018

Meteorological Element

Figure of the Month

Departure from Normal*

Mean Daily Maximum Air Temperature

28.0 degrees C

0.2 degree above normal

Mean Air Temperature

25.3 degrees C

0.2 degree below normal

Mean Daily Minimum Air Temperature

23.4 degrees C

0.3 degree below normal

Mean Dew Point Temperature

18.7 degrees C

1.5 degrees below normal

Mean Relative Humidity

69 %

4 % below normal

Mean Cloud Amount

59 %

1 % above normal

Total Rainfall

104.3 mm

3.4 mm above normal

Number of hours of Reduced VisibilityΔ

17 hours

113.5 hours below normal§

Total Bright Sunshine Duration

181.9 hours

12.0 hours below normal

Mean Daily Global Solar Radiation

14.75 Megajoule / square metre

0.7 Megajoule above normal

Total Evaporation

114.1 mm

9.8 mm below normal

Remarks :

All measurements were made at the Hong Kong Observatory except sunshine,
solar radiation and evaporation which were recorded at King's Park
Meteorological Station and visibility which was observed at the Hong
Kong International Airport.

Δ

The visibility readings at the Hong Kong International Airport are based on hourly observations by professional meteorological observers in 2004 and before, and average readings over the 10-minute period before the clock hour of the visibility meter near the middle of the south runway from 2005 onwards. The change of the data source in 2005 is an improvement of the visibility assessment using instrumented observations following the international trend.
Before 10 October 2007, the number of hours of reduced visibility at the Hong Kong International Airport in 2005 and thereafter displayed in this web page was based on hourly visibility observations by professional meteorological observers. Since 10 October 2007, the data have been revised using the average visibility readings over the 10-minute period before the clock hour, as recorded by the visibility meter near the middle of the south runway.

* Departure from 1981 - 2010 climatological normal, except for number of hours of reduced visibility

§ Departure from mean value between 1997 and 2017

Remarks :

Extremely high: above 95th percentile
Above normal: between 75th and 95th percentile
Normal: between 25th and 75th percentile
Below normal: between 5th and 25th percentile
Extremely low: below 5th percentile
Percentile and 5-day running average values are
computed based on the data from 1981 to 2010